1. Field of the Invention
The present invention relates generally to image projection apparatuses and circuit-board retaining structures.
2. Description of the Related Art
Some types of image projection apparatuses project an image onto a projection surface such as a screen by directing light from a light source to an image display device, such as a liquid crystal panel or a digital micro-mirror device (DMD), and projecting light modulated by the image display device according to the image onto the projection surface. To perform image projection in this manner, such an image projection apparatus includes at least a circuit board on which an image display device mounted and a control circuit board configured to control the image display device and the like. These circuit boards are electrically connected to each other via a connector.
There is a demand for projectors as image projection apparatuses to accomplish projecting a large screen image while minimizing projection space required outside the projector. To increase a projection screen size while reducing projection space outside an image projection apparatus, it is desirable to place as large a portion of an optical path of imaging light which forms an image to be projected as possible inside the projector. An image projection apparatus including such an optical system is disclosed in Japanese Patent No. 4210314. Adopting such an optical system allows reducing projection space outside an image projection apparatus and, furthermore, reducing a volume size of the image projection apparatus. However, a problem can arise when an image projection apparatus including an image display device such as a DMD is used. This type of image projection apparatus typically has the following configuration: a DMD circuit board including the image display device is positioned horizontally; and a main circuit board which controls the image projection apparatus is positioned vertically and connected to the DMD circuit board via a connector. If electrical noise is undesirably generated at a portion near the connector, a shield structure will be added to the image projection apparatus to prevent external leakage of the noise. As a result, even though the volume size of the image projection apparatus can be reduced by virtue of the optical system configuration described above, addition of the shield structure increases the apparatus in size.
Japanese Laid-open Patent Publication No. 02-161798 discloses a structure for reducing noise of a main circuit board and a sub circuit board connected to each other via a connector. In this structure, the main circuit board and the sub circuit board are arranged parallel to each other and each of the circuit boards is ground connected to a chassis interposed therebetween.
However, an image display device such as a DMD and other circuit boards are typically arranged perpendicular to each other.
In view of the above circumstances, there is a need to provide an image projection apparatus which generates less electrical noise than conventional image projection apparatuses.
It is an object of the present invention to at least partially solve the problem in the conventional technology.